The present invention relates to a method for producing components from a blank made of a deep-drawable material, particularly steel, using a free-flowing action medium.
Single blanks formed with the aid of fluid action media, hydroformed welded blanks or similar hollow bodies are suitable for producing complex components with improved properties and for optimizing the properties of the respective blank material used. To form simple blanks with the aid of fluid action media, the final form of the blanks is achieved using a stamp or a comparable forming tool (stamp or matrix) which works against a supporting pressure applied by a fluid cushion. In contrast, hydroforming is carried out by applying a high pressure to a cavity filled with a pressure fluid present between the blanks and/or in the hollow body. In this way, the workpieces are pressed by the so generated internal pressure into a form predetermined by the surrounding matrix.
In many cases it is necessary to produce intermediate forms to generate deep drawn parts or hydroformed parts having complex geometries, since the final contour may not be generated in one forming step. In this case, the intermediate form is carried out in tools which operate independently from the tool used to execute the final form. This partitioning of the tools and of the working steps elevates significantly the costs connected to the production of this type of components.
Intermediate forms can be also fashioned through hydromechanical forming. Accordingly, the blanks are preformed in the forming tool by the action medium before the execution of the main forming. The actual finish forming, during which the final form of the workpiece is achieved, occurs only after the preforming step is finished. For this to occur, however, the preforming geometry must correspond to the outline of the forming tool element. Although this procedure has been shown to be unfavorable with regard to the subsequent main forming, this disadvantage balances out the advantage that greater changes in form in the center of the component could be obtained, so that targeted hardenings may be generated and better exploitation of the properties of the materials could be obtained.
The object of the present invention is to provide a method to produce components having complex forms while optimizing the properties of the material used.
This object is achieved according to the present invention by a method in which the following steps are performed:
clamping the blank in a forming device, in which the blank has the action medium applied to it on at least one side;
preforming the blank by elevating the pressure exercised by the action medium in restricted areas of the blank""s surface which represent only portions of a section of the blank surface from which the final form of the component is generated, and
finish forming the preformed blank using a forming tool.
According to the present invention, partially preformed semi-finished products are generated from the blank in a first working step in a suitable forming device using free-flowing action media. The final form of the component is then generated from this preformed semi-finished product. In this case, the preforming only occurs in one limited region of the blank at a time. In contrast to multi-step drawing of components, the preforming is not used, for example, to implement specific form elements which are further shaped to their final form. Rather, a preform is generated and optimally prepared with consideration to the required properties of the component to be finally produced, to the material deformation and distribution, and with consideration to the exploitation of the material properties. Therefore, according to the present invention, the preform is only generated in those regions where it is required with consideration to the geometric properties (development) and/or to the component-specific properties (strength).
The blanks may be preformed in accord with the requirements of the final product, with or without the aid of a counter-mold. Preforming without a counter-mold has the advantage that the material constituting the blank may flow unimpeded during the preforming, so that, for example, an optimized strength of the preform may be achieved. In addition, the use of a counter-mold has the advantage that the preform may also be optimally prepared with consideration to the spatial arrangement of the final form to be generated. In this case, a balance between free forming and forming entirely in a counter-mold is possible in that only a part of the preformed region of the blank presses against the counter-mold, while free deformation occurs in other regions.
The generation of the component in its final form is preferably executed against a supporting pressure exercised by an action medium. In this way, an exactly shaped, high-quality component with optimized mechanical properties and a good visual appearance may be carefully produced with careful processing.
The blanks preformed according to the present invention may be connected to one another before the finish forming of the component into its final form. In this way, it is possible to manufacture particularly large-area components, or components in which the material distribution and/or the thickness of the material present in the regions of the various blanks is intentionally tailored to the loads of the single components. In this way, the blanks may be connected to one another using material bonding, frictional connection and/or form fit. Alternatively, blanks lying loosely on one another may also be jointly brought into the final form after preforming.
Hollow shapes may also be easily implemented using the method according to the present invention if there is a cavity between the preformed blanks laid on one another and possibly connected to one another. The forms generated in this way are particularly suitable to be executed into their final forms by hydroforming, whereby a high pressure is applied to the cavity during the finish forming of the blanks into their final forms.